1. No. This will not work at all, and you risk damaging the equipment. You also risk damaging yourself. Two sets of current going through the same area can cause some "interesting" responses from the muscles and nerves.
2. You might create "beat" frequencies as the two frequencies interact with unknown consequences, It might be something that is worth exploring as a controlled experiment with specific frequencies in a laboratory setting. It is too risky for any of us to recommend.
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